Disadvantages of PNG

It would be grand if there were no downsides to using .png, but, alas, there
are. Some are more substantial than others.

No Support for Animation

This is a very minor downside. Unlike the .gif file type that supports both
still and moving images, .png supports only still images. A sister file type,
.mng, for Multiple-image Network Graphic, has been created to replace animated
.gifs.

Incomplete Support

Whenever you use something new in your Web work, you run the risk that
you'll lose part of your viewership. Both the current versions of Netscape
and Internet Explorer support .png; however, older versions of both browsers and
some third party browsers still do not. If your business depends on your image
being seen, it's not the time to make a political statement with a
.pnggo ahead and use the GIF or JPEG image formats.